A quadrifilar helical antenna (QHA) is comprised of four separate helices with four independent ports. A QHA may be constructed from metal wires, conductive strips or printed on a dielectric sheet that is cylindrically wrapped to generate, with a suitable feeding network, circular polarization radiation. QHAs have been used for antenna diversity, land mobile satellite (LMS) communication, as well as other satellite communications and navigation systems.
QHAs have been used as circularly polarized (CP) single port antenna elements in two-element, three-element or two-by-two element arrays for application in multiple-input multiple-output (MIMO) systems. In MIMO applications, antenna elements with only two independent physical ports are typically implemented. A four-port QHA antenna element had been demonstrated in a single antenna MIMO system in comparison to four spatially-separated half-wave dipoles MIMO system. Using multi-port QHAs as antenna elements in an antenna array may help to reduce the total size of the antenna array, which would be useful for miniaturization purposes as well as providing reduction in cost.
An example multi-port QHA design is described in U.S. patent application Ser. No. 14/839,192, entitled “Multi-Filar Helical Antenna”, filed Aug. 28, 2015, the entirety of which is hereby incorporated by reference. It would be useful to modify this design, for example to reduce the antenna height, improve the radiation patterns, reduce coupling between ports and/or maintain a relatively wide impedance bandwidth.